1. Field of the Invention
The present invention relates to a method of fabricating an optical waveguide through which a light signal propagates and a method of manufacturing an optical transmitting/receiving apparatus having such an optical waveguide.
2. Description of the Related Art
As the technology in an IC (Integrated Circuit) and an LSI (Large Scale Integrated) circuit progresses, their operating speed and scale of integration are improving and, for example, the higher performance of a microprocessor and the larger capacity of a memory chip are rapidly being achieved. Hitherto, transmission of information in relatively short distance, for example, between boards in a device or between chips on a board is carried out mainly via an electric signal. In order to further improve the performance of an integrated circuit in the future, it is necessary to increase the transmission rate of a signal and the density of signal wiring. In the electric signal wiring, however, it is difficult to increase the transmission rate of a signal and the density of signal wiring, and a problem of a signal delay by a time constant of CR (C: capacitance of wiring and R: resistance of wiring) of wires arises. Since an increase in transmission rate of the electric signal and an increase in density of the electric signal wiring cause EMI (Electromagnetic Interference) noises, it is indispensable to take countermeasures against the problems.
Optical wiring (optical interconnection) attracts a considerable attention as a means for solving the problems. The optical wiring is considered to be applicable to various situations such as the connection between devices, between boards in a device, or between chips on a board. Among them, for transmission of signals over relatively short distances such as transmission between chips, it is considered to be suitable to build a light transmission communication system. In the system, an optical waveguide is formed on a substrate on which chips are mounted and is used as a transmission line. In order to spread the light transmission communication system using the optical waveguide as a transmission line, it is important to establish a process of forming the optical waveguide.
As a known conventional method of fabricating an optical waveguide, a method of forming an optical waveguide made of quartz or a high polymer material such as PMMA (Polymethyl Methacrylate) or polyimide on a flat substrate such as a silicon substrate or glass substrate is known. Since the optical waveguide is formed on a flat substrate in the method, the optical waveguide with a slight loss in light propagation can be easily formed.
In the optical transmission communication system using the optical waveguide as a transmission line, however, a light emitting device for converting an electric signal into a light signal, a photodetecting device for converting a light signal into an electric signal, an IC chip for transmitting an electric signal between the light emitting device and the photodetecting device, and the like have to be provided. Supply of power to the devices and transfer of various control signals of relatively low speed have to be performed by electric signals as ever.
It is therefore indispensable to provide thin film multilayer wiring as electric signal wiring on a substrate. However, increasing the area in which the electric signal wires are formed to a normal wiring substrate size (tens cm per side) or a module size (a few cm per side) costs too much, and is difficult to be put into practice, thereby causing a problem.
In order to solve the problem, it can be considered to form an optical waveguide on a printed wiring board on which electrical parts can be mounted. On the surface of such a wiring board manufactured by thick film process, however, a metal thick film formed by plating or the like is provided and the surface is considerably uneven. When an optical waveguide is formed on the printed wiring board, consequently, the shape of the optical waveguide is influenced by the surface unevenness of the board. It causes a problem such that a light propagation loss in the optical waveguide increases and the dimension accuracy deteriorates.
Further, in the case of forming the optical waveguide on the wiring board, in wet etching, cleaning and the like, a process of immersing the whole board in an acid or alkali solution, an organic solvent, or the like is necessary. Consequently, there is a problem such that the board may be damaged. There is also the possibility that the board is damaged in the event of dry etching and heat treatment at high temperature. It is therefore difficult to use an electric wiring board formed by a thick film process such as a printed wiring board as a board. An expensive board having characteristics such as high heat resistance has to be used.
The present invention has been achieved in consideration of the problems and its object is to provide a method of easily forming an optical waveguide capable of holding an excellent light propagating characteristic irrespective of the kind of a supporting board.
According to the invention, there is provided a method of manufacturing an optical waveguide by forming an optical waveguide on a first substrate side and then transferring the optical waveguide on the first substrate side to a second substrate side, comprising: a step of forming a peelability promoting film for promoting peelability between the first substrate and a layer to be formed on the first substrate; a step of forming at least an optical waveguide on the peelability promoting film; a step of fixing the optical waveguide supported by the first substrate and the second substrate to each other; and a step of peeling the first substrate off the optical waveguide.
According to the invention, there is also provided a method of manufacturing an optical transmitting/receiving apparatus having an optical waveguide by forming the optical waveguide on a first substrate side and transferring the optical waveguide from the first substrate side to a second substrate side, comprising: a step of forming a peelability promoting film for promoting peelability between the first substrate and a layer to be formed on the first substrate; a step of forming at least an optical waveguide on the peelability promoting film; a step of fixing the optical waveguide supported by the first substrate and the second substrate to each other; a step of peeling the first substrate off from the optical waveguide; a step of forming at least one of a light emitting device for converting an electric signal into a light signal and a photodetecting device for converting a light signal into an electric signal on the second substrate; and a step of forming an integrated circuit for transferring/receiving an electric signal to/from at least one of the light emitting device and the photodetecting device on the second substrate.
In the method of manufacturing the optical waveguide and the method of manufacturing the optical transmitting/receiving apparatus according to the invention, the peelability promoting film and the optical waveguide are sequentially formed on the first substrate. After that, the optical waveguide and the second substrate are fixed to each other. By peeling the first substrate off the optical waveguide by using the peelability promoting film, the optical waveguide is transferred from the first substrate to the second substrate.
Other and further objects, features and advantages of the invention will appear more fully from the following description.